Internal combustion engine and method for manufacturing internal combustion engine

ABSTRACT

A cylinder block of an internal combustion engine includes an oil drain hole that opens in a lower surface of the cylinder block. An oil pan is fixed to a lower part of the cylinder block and configured to collect oil. A balancer device is arranged inside the oil pan below a crankshaft. A baffle plate is flat and arranged inside the oil pan between the crankshaft and the balancer device covering the balancer device from above. An oil flow passage extends through the baffle plate in a thickness-wise direction. The oil flow passage is arranged in the baffle plate at a location overlapped with an oil falling path that extends from the oil drain hole to a bottom surface of the oil pan.

BACKGROUND 1. Field

The following description relates to an internal combustion engine and a method for manufacturing the internal combustion engine.

2. Description of Related Art

Japanese Laid-Open Patent Publication No. 06-017879 discloses a typical internal combustion engine having an oil pan arranged below a cylinder block. Crank caps are fixed to the lower surface of the cylinder block inside the oil pan. A crankshaft is rotatably supported between the cylinder block and the crank caps. Further, a balancer device is located below the crank caps inside the oil pan. The balancer device includes a balancer shaft, which rotates in synchrony with the crankshaft, and an unbalance mass, which is fixed to the balancer shaft. The balancer shaft rotates with the unbalance mass to reduce vibration of the crankshaft generated by the movement of the pistons.

Further, a flat baffle plate is arranged between the crankshaft and the balancer shaft inside the oil pan. The baffle plate extends over substantially the entire open area of the oil pan so as to cover the balancer device from above and divide the inside of the oil pan into two in the vertical direction.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

An internal combustion engine includes a cylinder block, an oil pan, a balancer device, a baffle plate, and an oil flow passage. The cylinder block includes an oil drain hole that opens in a lower surface of the cylinder block. The oil pan is fixed to a lower part of the cylinder block and configured to collect oil. The balancer device is arranged inside the oil pan below a crankshaft. The baffle plate is flat and arranged inside the oil pan between the crankshaft and the balancer device covering the balancer device from above. The oil flow passage extends through the baffle plate in a thickness-wise direction and is arranged at a location in the baffle plate overlapped with an oil falling path extending from the oil drain hole to a bottom surface of the oil pan.

With the above structure, oil drained from the oil drain hole flows through the oil flow passage located in the oil falling path and reaches a region located downward from the baffle plate without being interfered with by the baffle plate. Accordingly, excess oil does not collect on the upper surface of the baffle plate. This prevents the oil on the upper surface of the baffle plate from being drawn toward the rotating crankshaft.

A typical cylinder block of an internal combustion engine includes an oil drain hole that guides oil, which has lubricated various parts of the internal combustion engine, into an oil pan. In the typical internal combustion engine in the above patent document, the baffle plate divides the inside of the oil pan into two in the vertical direction. Accordingly, the oil drained from the oil drain hole is likely to collect on the upper surface of the baffle plate. If excessive oil collects on the upper surface of the baffle plate, this can cause undesirable situations such that the oil is drawn toward the rotating crankshaft and produces air bubbles or such that the collected oil resists rotation of the crankshaft. The above-described structure solves such problems.

With the internal combustion engine of the aforementioned example, the oil flow passage is located directly below an opening of the oil drain hole in a lower surface of the cylinder block in a vertical direction in a state in which the internal combustion engine is installed in a vehicle.

With the above structure, the oil drained from the oil drain hole continues to fall through the oil flow passage and reaches a region located downward from the baffle plate. Thus, even without any special structure that guides oil to the oil flow passage, the oil effectively reaches the region located downward from the baffle plate.

An oil pan using the above-described configurations is defined.

A method for manufacturing the internal combustion engine according to the above-described configurations is defined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an internal combustion engine according to one embodiment.

FIG. 2 is a top view of a crankcase of the internal combustion engine shown in FIG. 1.

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art.

An internal combustion engine according to an embodiment will now be described with reference to FIGS. 1 and 2. In the present embodiment, the internal combustion engine is installed in a vehicle. Further, a top-bottom direction in a state in which the internal combustion engine is installed in the vehicle will be referred to as a vertical direction.

As shown in FIG. 1, an internal combustion engine 10 includes a substantially box-shaped cylinder block 20. Tubular cylinders 22 (only one shown in FIG. 1) are defined in the cylinder block 20. The cylinders 22 each have an axis extending in the vertical direction. The cylinders 22 are arranged in a single row in an axial direction of a crankshaft 100 of the internal combustion engine 10. The cylinders 22 each include a piston (not shown) that reciprocates in the cylinder 22.

In the cylinder block 20, a hollow portion 23 is defined below each cylinder 22. The hollow portion 23 extends to a lower surface of the cylinder block 20. That is, the hollow portion 23 connects each cylinder 22 and the portion below the lower surface the cylinder block 20. In each hollow portion 23, a connecting rod (not shown) is movably coupled to the piston arranged in the corresponding cylinder 22. The connecting rod is coupled to the crankshaft 100 so that when the engine is running, the connecting rod converts reciprocation of the piston in the vertical direction as viewed in FIG. 1 into rotation of the crankshaft 100.

As described above, the hollow portions 23 are located next to one another. Accordingly, partition walls 21 are arranged between adjacent hollow portions 23 in the cylinder block 20 to define the hollow portions 23. Each partition wall 21 includes a lower surface defining a bearing 26 that is semicircular in a front view and recessed upward. When a direction that is orthogonal to both the axial direction of the crankshaft 100 and the vertical direction is referred to as a widthwise direction of the internal combustion engine 10, the bearing 26 is located in the central part of the partition wall 21 in the widthwise direction of the internal combustion engine 10.

An oil drain hole 24 is defined in the cylinder block 20 toward one side (left side in FIG. 1) in the widthwise direction of the internal combustion engine 10 from the cylinders 22 and the hollow portion 23 extending in the vertical direction. The oil drain hole 24 opens in the lower surface of the cylinder block 20. The oil drain hole 24 is in communication with the inside of a cylinder head (not shown) so that oil (lubrication oil) falls from the cylinder head through the oil drain hole 24.

Crank caps 30 are fixed to the lower surfaces of the partition walls 21 in the cylinder block 20. Each crank cap 30 is a substantially rectangular plate and has substantially the same thickness as the partition wall 21. The crank cap 30 has a dimension in the longitudinal direction (leftward and rightward directions in FIG. 1) that is set to be smaller than the dimension of the partition wall 21 in the widthwise direction of the internal combustion engine 10. The crank cap 30 is arranged so that the longitudinal direction of the crank cap 30 corresponds to the widthwise direction of the partition wall 21 and the internal combustion engine 10 and the thickness-wise direction of the crank cap 30 corresponds to that of the partition wall 21. The crank cap 30 has an end at one side in the longitudinal direction (left side in FIG. 1) that is located toward the middle in the widthwise direction of the internal combustion engine 10 from the oil drain hole 24 of the cylinder block 20.

Each crank cap 30 includes an upper surface defining a bearing 32 that is semicircular in a front view and recessed downward. Further, the bearings 32 of the crank caps 30 are arranged to oppose the bearings 26 of the partition walls 21 in the cylinder block 20. In the widthwise direction of the internal combustion engine 10, each crank cap 30 includes bolts B1 inserted through the crank cap 30 from below at opposite sides of the bearing 32. The bolts B1 extend through the crank cap 30 in the vertical direction and are fastened to the cylinder block 20. That is, the crank caps 30 are fixed to the cylinder block 20 by the bolts B1.

The crankshaft 100 is rotatably supported between the bearings 32 of the crank caps 30 and the bearings 26 of the partition walls 21 in the cylinder block 20.

An oil pan 40, which substantially has the form of a quadrangular box, is fixed to the lower surface of the cylinder block 20. The oil pan 40 includes a crankcase 50, which has the form of a quadrangular box and is open upward, and a reservoir case 60, which has the form of a quadrangular box and is open upward. The reservoir case 60 is coupled to a lower side of the crankcase 50 and opens upward.

The crankcase 50 includes a bottom wall 52 and a peripheral wall 51. The bottom wall 52 has the form of a substantially rectangular plate, and the peripheral wall 51 forms a rectangular hollow post that extends upward from the periphery of the bottom wall 52. The peripheral wall 51 has an upper end surface that extends along the periphery of the lower surface of the cylinder block 20. The crankcase 50 is fixed to the cylinder block 20 so that the upper end surface of the peripheral wall 51 is in contact with the periphery of the lower surface of the cylinder block 20. As described above, the crank caps 30 are fixed to the lower surfaces of the corresponding partition walls 21 of the cylinder block 20. Accordingly, the peripheral wall 51 of the crankcase 50 surrounds the crank caps 30.

As shown in FIGS. 1 and 2, the bottom wall 52 includes an opening 52 a that extends through the bottom wall 52 in the vertical direction. In the present embodiment, the opening 52 a is rectangular in a plan view. The opening 52 a extends over most of the bottom wall 52. Further, the opening 52 a is located so that in a plan view of the internal combustion engine 10 taken from above, the opening 52 a is set to entirely include the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20.

As shown in FIG. 1, bearing formation portions 54, which are substantially box-shaped, project upward from the bottom wall 52. As shown in FIG. 2, the bearing formation portions 54 are arranged at the two axial sides of the crankshaft 100 sandwiching the opening 52 a. The two bearing formation portions 54 are located at corresponding positions in the widthwise direction of the internal combustion engine 10 and oppose each other in the axial direction of the crankshaft 100. As shown in FIG. 1, the bearing formation portion 54 includes a bearing 54 a that is semicircular in a front view and recessed downward from the upper surface of the bearing formation portion 54.

Balancer caps 42, which are substantially box-shaped, are fixed to the upper surfaces of the bearing formation portions 54. The balancer caps 42 each include a bearing 42 a that is semicircular in a front view and recessed upward from the lower surface of the balancer cap 42. The balancer cap 42 is arranged so that the bearing 42 a opposes the bearing 54 a of the corresponding bearing formation portion 54. The balancer cap 42 includes bolts B2 that are inserted through the balancer cap 42 from above at opposite sides of the bearing 42 a in the balancer cap 42. The bolts B2 extend through the balancer cap 42 in the vertical direction and are fastened to the bearing formation portion 54. That is, the balancer caps 42 are fixed to the bearing formation portions 54 by the bolts B2.

A balancer shaft 82, which extends in the axial direction of the crankshaft 100, is rotatably supported between the bearings 42 a of the balancer caps 42 and the bearings 54 a of the bearing formation portions 54.

As shown in FIG. 2, a driven gear 84 is arranged outward in the axial direction of the crankshaft 100 from one of the bearing formation portions 54 of the balancer shaft 82. The driven gear 84 is fixed to the balancer shaft 82 and rotated integrally with the balancer shaft 82. The driven gear 84 is drive-coupled to the crankshaft 100 by a gear (not shown). When the crankshaft 100 is rotated, the balancer shaft 82 is synchronously rotated.

An unbalance mass 86 is arranged outward in the axial direction of the crankshaft 100 from the driven gear 84 of the balancer shaft 82. The unbalance mass 86 is fixed to the balancer shaft 82 and rotated integrally with the balancer shaft 82. The unbalance mass 86 is, for example, semicircular (sectoral) and has a center of mass that is eccentric from the axis of the balancer shaft 82. When the balancer shaft 82 is rotated, the balancer shaft 82 rotates in a state in which the center of mass of the balancer shaft 82 is eccentric to the rotation center. This reduces vibration of the crankshaft 100 generated by reciprocation of the pistons. The balancer shaft 82, the driven gear 84, and the unbalance mass 86 form a balancer device 80. The balancer device 80 is arranged on the bottom wall 52 of the crankcase 50 and is thereby located below the crankshaft 100 that is located in the lower surface of the cylinder block 20 inside the oil pan 40.

As shown in FIG. 1, the reservoir case 60 collects oil. Although not shown in the drawings, the reservoir case 60 includes an inlet of an oil pump that draws out oil from the reservoir case 60. The oil pump is actuated so that oil is supplied to various parts (for example, camshaft accommodated in cylinder head) of the internal combustion engine 10 that require lubrication.

As shown in FIG. 1, a baffle plate 70 is arranged inside the oil pan 40 between the crankshaft 100 and the balancer device 80. Specifically, as shown in FIGS. 1 and 2, bosses 56 that have the form of rectangular posts project upward from the bottom wall 52 of the crankcase 50. There are a total of four bosses 56, two on each of the two sides of the opening 52 a in the widthwise direction of the internal combustion engine 10. Each of the four bosses 56 includes an upper end surface projecting upward from the balancer shaft 82 that is supported by the two bearing formation portions 54. The baffle plate 70, which is flat, is coupled to the upper end surfaces of the four bosses 56. The baffle plate 70 includes bolts B3 that are inserted into the bosses 56 from above. The bolts B3 are each extended through the baffle plate 70 in the vertical direction and fastened to the corresponding one of the four bosses 56. That is, the balancer caps 42 are fixed to the four bosses 56 by the bolts B3.

The baffle plate 70 is rectangular and substantially covers the entire opening 52 a. The baffle plate 70 is located between the two bearing formation portions 54 in the axial direction of the crankshaft 100. The upper end surfaces of the four bosses 56 project upward from the balancer shaft 82 so that the baffle plate 70 covers the balancer shaft 82 from above.

The baffle plate 70 includes an oil flow passage 72 located directly below the oil drain hole 24 of the cylinder block 20 in the vertical direction. The oil flow passage 72 is an opening extending through the baffle plate 70 in a thickness-wise direction. In the present embodiment, the oil flow passage 72 is shaped as a square cutout and arranged in one of the four corners of the rectangular baffle plate 70. In a plan view of the internal combustion engine 10, the oil flow passage 72 exposes a region of the opening 52 a in the crankcase 50 (shaded region in FIG. 2) from the baffle plate 70. The exposed region has an area that is set to be greater than the area of the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. Further, in a plan view of the internal combustion engine 10, the entire region of the opening 24 a of the oil drain hole 24 is included in the exposed region.

The advantages of the present embodiment will now be described.

(1) Oil collected in the reservoir case 60 is circulated through the internal combustion engine 10. Specifically, when the oil pump is actuated, oil is supplied to various parts of the internal combustion engine 10 for lubrication and reaches the oil drain hole 24 of the cylinder block 20. Then, the oil falls through the oil drain hole 24 and is drained from the oil drain hole 24 to the crankcase 50. The oil drained from the oil drain hole 24, as shown by arrow A in FIG. 1, continues to fall in the vertical direction into the reservoir case 60. Thus, in the present embodiment, the portion directly below the oil drain hole 24 in the perpendicular direction is an oil falling path that extends from the oil drain hole 24 to the bottom surface of the reservoir case 60.

In the present embodiment, the oil flow passage 72 is located directly below the oil drain hole 24 in the vertical direction (at position overlapped with oil falling path) in the baffle plate 70. Accordingly, the oil drained from the oil drain hole 24 flows through the oil flow passage 72 located in the oil falling path. Then, the oil reaches a region located downward from the baffle plate 70 without being interfered with by the baffle plate 70 and returns to the reservoir case 60. Thus, excessive oil does not collect on the upper surface of the baffle plate 70. This prevents a situation where the oil on the upper surface of the baffle plate 70 is drawn toward the rotating crankshaft 100.

(2) If the oil flow passage 72 is not located directly below the oil drain hole 24 in the vertical direction, the oil drained from the oil drain hole 24 may fall directly onto the upper surface of the baffle plate 70 and collect on the upper surface. Thus, if the oil flow passage 72 is not located directly below the oil drain hole 24 in the vertical direction, a guide wall can be arranged in the crankcase 50 to guide the oil to the oil flow passage 72. However, the arrangement of such a guide wall will result in the crankcase 50 having a complicated shape.

In this regard, in the present embodiment, the oil flow passage 72 is located directly below the oil drain hole 24 in the perpendicular direction. Thus, the oil falling from the oil drain hole 24 continues to fall through the oil flow passage 72 and reaches a region located downward from the baffle plate 70. Thus, oil effectively reaches a region located downward from the baffle plate 70 without any special structure that guides oil to the oil flow passage 72. Accordingly, in the above-described embodiment, the crankcase 50 has a simple structure. For example, this may simplify the structure of a mold used to manufacture the crankcase 50.

(3) If the region of the opening 52 a in the crankcase 50 exposed from the baffle plate 70 (shaded region in FIG. 2) has a smaller area than the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. In this case, in a plan view of the internal combustion engine 10, part of the baffle plate 70 would be located in the range of the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. That is, part of the baffle plate 70 would be located directly below part of the opening 24 a of the oil drain hole 24. In such a case, part of the oil drained from the oil drain hole 24 will not reach the oil flow passage 72 and be interfered with by the upper surface of the baffle plate 70. Such oil will collect on the upper surface of the baffle plate 70.

In this respect, in the above-described embodiment, the region of the opening 52 a in the crankcase 50 exposed from the baffle plate 70 (shaded area in FIG. 2) has a greater area than the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. Accordingly, the baffle plate 70 is not located directly below the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. This ensures that the oil drained from the oil drain hole 24 reaches the region located downward from the baffle plate 70 without being interfered with by the baffle plate 70.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without technically contradicting each other or departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

The cutout, which corresponds to the oil flow passage 72, does not need to have a square shape and may have the shape of a polygon other than a square or an arcuate shape. Further, the oil flow passage 72 may be configured as a through hole extending through the baffle plate 70 in the thickness-wise direction. The through hole may have any shape such as polygonal or an arcuate shape in a plan view. More specifically, the oil flow passage 72 may have any shape as long as it extends through the baffle plate 70 in the thickness-wise direction at a location overlapped with the oil falling path, which extends from the oil drain hole 24 of the baffle plate 70 to the bottom surface of the reservoir case 60.

The portion of the opening 52 a in the crankcase 50 exposed from the baffle plate 70 (shaded area in FIG. 2) may have a smaller area than the opening 24 a of the oil drain hole 24 in the lower surface of the cylinder block 20. When there is no significant difference in area between these regions, most of the oil drained from the oil drain hole 24 will reach the oil flow passage 72 without being interfered with by the baffle plate 70. Further, even when there is a large difference in area between these regions, at least some of the oil will reach the region located downward from the baffle plate 70 through the oil flow passage 72.

Depending on the position of the internal combustion engine 10 when installed in a vehicle, the oil falling path may not be located below the oil drain hole 24 in the vertical direction. For example, the oil falling path may be a passage extending from the opening 24 a of the oil drain hole 24 via the lower surface of the cylinder block 20 and the inner wall surface of the crankcase 50 to the bottom surface of the reservoir case 60. As long as a guide wall and the like is arranged to guide oil toward the internal peripheral wall of the crankcase 50 and form the oil falling path, the oil flow passage 72 (cutout) may be arranged in the baffle plate 70 at a location overlapped with the falling passage.

The baffle plate 70 may have any form or size. Nonetheless, the baffle plate 70 needs to be a plate that covers most of the balancer shaft 82. The baffle plate 70 may be modified to cover the driven gear 84 and the unbalance mass 86 in addition to the balancer shaft 82. In this case, an opening may be arranged at a location above the driven gear 84 in the baffle plate 70 to allow the driven gear 84 to mesh with another gear. Alternatively, a plurality of openings may be arranged in the baffle plate 70 above the balancer shaft 82 at one or more locations so that the balancer shaft 82 is partially exposed from the baffle plate 70. The openings do not have to be located at locations above the balancer shaft 82 on the baffle plate 70.

A funnel-like wall having a diameter that increases upward and projects from the upper surface of the baffle plate 70 may be arranged around the oil flow passage 72 on the upper surface of the baffle plate 70. Arrangement of such a wall allows oil to easily reach the oil flow passage 72.

The upper surface of the baffle plate 70 may be a surface inclined downward to the oil flow passage 72. In this case, even when oil is scattered onto the upper surface of the baffle plate 70, the oil is guided to the oil flow passage 72. This prevents excess oil from collecting on the upper surface of the baffle plate 70.

The shape, location, and number of the bosses 56 that support the baffle plate 70 may be changed as long as the bosses 56 support the baffle plate 70 above the balancer shaft 82.

The shape, location, and number of the bearing formation portions 54 and the balancer caps 42 that support the balancer shaft 82 may be changed as long as the bearing formation portions 54 and the balancer caps 42 rotatably support the balancer shaft 82 in parallel with the crankshaft 100.

The opening 52 a of the crankcase 50 may have any shape and area. Nonetheless, the opening 52 a needs to allow for recirculation of oil to the reservoir case 60. The opening 52 a may be divided into two or more sections.

The mechanism that synchronizes and rotates the balancer shaft 82 and the crankshaft 100 is not limited to the meshed gears. For example, a belt or a chain may be used to synchronize and rotate the balancer shaft 82 and the crankshaft 100.

The structure of the balancer device 80 may be modified as long as the vibration of the crankshaft 100 generated from reciprocation of the pistons can be reduced. For example, the location or number of the driven gear 84 and the unbalance mass 86 may be changed. Further, there may be two or more balancer shafts 82 including the unbalance mass 86.

In the cylinder block 20, the oil drain hole 24 may be located at the other side of the internal combustion engine 10 in the widthwise direction (right side in FIG. 1). In this case, the oil flow passage 72 is arranged at a position overlapped with the oil falling path, which extends from the oil drain hole 24, in the baffle plate 70.

One longitudinal end (left end as viewed in FIG. 1) of the crank cap 30 may be located closer to the edge of the internal combustion engine 10 in the widthwise direction than the oil drain hole 24 of the cylinder block 20. In this case, a through hole that is in communication with the oil drain hole 24 and extends through the crank cap 30 in a substantially vertical direction will be arranged at a location below the oil drain hole 24 in the crank cap 30. In this modified example, the through hole in the crank cap 30 forms part of the oil falling path.

The present invention may employ a ladder-frame structure in which the crank cap 30 has longitudinal ends that are both connected to the peripheral wall 51 of the crankcase 50.

The number of the cylinders 22 may be changed. In such a case, the number of the partition walls 21 and the number of the crank caps 30 will be changed in accordance with the number of the cylinders 22.

The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

What is claimed is:
 1. An internal combustion engine, comprising: a cylinder block including an oil drain hole that opens in a lower surface of the cylinder block; an oil pan fixed to a lower part of the cylinder block and configured to collect oil; a balancer device arranged inside the oil pan below a crankshaft; a flat baffle plate arranged inside the oil pan between the crankshaft and the balancer device covering the balancer device from above; and an oil flow passage extending through the baffle plate in a thickness-wise direction and arranged at a location in the baffle plate overlapped with an oil falling path extending from the oil drain hole to a bottom surface of the oil pan.
 2. The internal combustion engine according to claim 1, wherein the oil flow passage is located directly below an opening of the oil drain hole in a lower surface of the cylinder block in a vertical direction in a state in which the internal combustion engine is installed in a vehicle.
 3. An oil pan, comprising: a crankcase fixed to a lower part of a cylinder block of an internal combustion engine and configured to collect oil, wherein the cylinder block includes an oil drain hole that opens in a lower surface of the cylinder block; a balancer device arranged inside the crankcase below a crankshaft; a flat baffle plate arranged inside the crankcase between the crankshaft and the balancer device to cover the balancer device from above; and an oil flow passage that extends through the baffle plate in a thickness-wise direction and is arranged at a location in the baffle plate overlapped with an oil falling path extending from the oil drain hole to a bottom surface of the crankcase.
 4. A method for manufacturing an internal combustion engine, the method comprising: providing a cylinder block including an oil drain hole that opens in a lower surface of the cylinder block; preparing an oil pan fixed to a lower part of the cylinder block and configured to collect oil; arranging a balancer device inside the oil pan downward from a crankshaft; arranging a flat baffle plate inside the oil pan between the crankshaft and the balancer device to cover the balancer device from above; and arranging an oil flow passage at a location in the baffle plate overlapped with an oil falling path extending from the oil drain hole to a bottom surface of the oil pan in the baffle plate, wherein the oil flow passage extends through the baffle plate in a thickness-wise direction. 